Apparatus for the production of synthetic plastics molds for metal casting small dental prosthetic parts, such as crowns and caps

ABSTRACT

In the production, by fluid pressure deformation of plastic foils, of molds for metal casting of small dental prosthetic parts, and in which a stump model is imbedded in a vessel attachable to a work plate of a foil deforming appliance, an insert, formed with a number of openings, is provided for attachment to the work plate. At least one pot-type vessel, having a supporting edge formed with fine air discharged channels, is inserted into an appropriate opening of the insert and a kneadable composition is placed in the vessel and shaped to extend somewhat conically above the support edge. The unprepared stump model is pressed into the composition and, after any necessary preparation of the stump model, fine channels are notched into the surface of the conically shaped portion of the composition to extend between the base of the stump model and the fine air discharge channels. Thereafter, a plastics foil is deformed into conforming relation with the model either by the application of fluid pressure or by vacuum drawing.

United States Patent Scheu 1 Feb. 22, 1972 [72] Inventor:

Rudolf Scheu, Burgberg 20, 5868 Letmathe, Westfalia, Germany [22] Filed:June 24,1970

[21] Appl. No.: 49,458

[30] Foreign Application Priority Data July 10, 1969 Germany ..P 19 34975.8

[52] US. Cl ..164/235, 164/7, 164/34, 164/160, 18/33, 18/35, 18/D1G. 62,l8/DlG. 60, 264/19, 264/92, 264/221 [51] Int. Cl ..A6lc 13/08, B22c7/02, B29c 1/02, B29c 17/00 [58] FieldofSearch ..164/6,7, 13,29, 34, 45,159, 164/160, 235; 18/19 F, 33, 34.1, 35, D16. 62, DIG. 60; 264/19, 92,221

[56] References Cited UNITED STATES PATENTS 2,985,914 5/1961 Miller..18/19 F 3,027,596 4/1962 Knowles. ..18/ 19 F 3,053,023 9/1962 Watts..18/19 F UX 3,065,511 11/1962 Leitzel ..164/45 3,151,369 10/1964Sullivan ..164/7 3,161,915 12/1964 Thiel ....18/19F 3,193,893 7/1965Ross et al ..164/45 X 3,290,418 12/1966 Best ....18/19 F X 3,307,2223/1967 Baldwin et a1. ..18/19 F IIIIIIIIIII A 3,351,123 11/1967 Payne..164/34 3,406,428 10/1968 Brown ..18/19 F 3,446,266 5/1969 Watts et al.....164/7 x 3,482,281 12/1969 Thiel ..18/19 F 3,532,776 10/1970 Kopp..164/7 x OTHER PUBLICATIONS Design Guide for Small Investment Castings,an editorial reprint from Precision Metal by Casting Engineers, Chicago,111.,

Tooling for Economic Investment Casting," an editorial reprint from TheTool and Manufacturing Engineer by Casting Engineers, Chicago, 111.,pages 322, 3/70.

Primary Examiner-J. Howard Flint, Jr. Attorney-McGlew and Toren [57]ABSTRACT In the production, by fluid pressure deformation of plasticfoils, of molds for metal casting of small dental prosthetic parts, andin which a stump model is imbedded in a vessel attachable to a workplate of a foil deforming appliance, an insert, formed with a number ofopenings, is provided for attachment to the work plate. At least onepot-type vessel, having a supporting edge formed with fine airdischarged channels, is inserted into an appropriate opening of theinsert and a kneadable composition is placed in the vessel and shaped toextend somewhat conically above the support edge. The unprepared stumpmodel is pressed into the composition and, after any necessarypreparation of the stump model, fine channels are notched into thesurface of the conically shaped portion of the composition to extendbetween the base of the stump model and the fine air discharge channels.Thereafter, a plastics foil is deformed into conforming relation withthe model either by the application of fluid pressure or by vacuumdrawing.

11 Claims, 11 Drawing Figures mmm I972 SHEET 1 OF 2 IN VEN TOR QUDOL FSCI-IEO FIG. 2C

PATENTEU EBZZ I 2 3,643,730

SHEET 2 OF 2 IN VE N TOR R0001.- SCI/EU 4 TTORWEVS APPARATUS FOR THEPRODUCTION OF SYNTHETIC PLASTICS MOLDS FOR METAL CASTING SMALL DENTALPROSTI-IETIC PARTS, SUCH AS CROWNS AND CAPS BACKGROUND OF THE INVENTIONIn the casting, in gold or white metal, of dental crowns and stump capsfor use in the mouth, initially wax molds, or, more recently, syntheticplastics molds, are produced on the model and are them imbedded inceramic compositions. In the subsequent heating of these ceramicmuffles, the wax or the synthetic plastics material melts and burnsaway, and the metal is injected into the resulting cavity by acentrifugal method of the like.

In the production of wax molds, which generally were used earlier, nodifficulties occurred if appropriate mechanical skill was utilized,because any contractions occurring in setting and which took effect inthe vertical dimension of the formed wax mold sleeve, such as lack ofshoulder edge fit, could be eliminated by the application of liquid wax,Today, the contraction of the metals after casting, which occurs in alldirections, is generally compensated by appropriately developedimbedding compositions which expand to the same extent due to theheating.

Synthetic plastics molds, generally used in modern technology, andusually produced by vacuum deep-drawing or by compressed airdeformation, have the outstanding advantage of stability during thefurther processing and imbedding. However, the longitudinally actingtraction, which cannot be eliminated, is a great disadvantage.

Attempts have been made to eliminate this drawback or disadvantage bythe use of what are called underlay foils," such as disclosed in GermanPat. No. (DAS) l,l26l,980, the lower foil being drawn out of the sleevebefore imbedding. However, since in this procedure the lower foilextends over the cutting or chewing surface to beyond the marginalshoulder of the model, the gain occurring in one direction is lost againin the direction perpendicular thereto, namely in the directionperpendicular to the marginal shoulder.

For this reason, more recently, pastes applied with small brushes havebeen used, and these leave the marginal shoulder of the models free aswell as having a compensating or equalizing effect only at the shrinkagepoints. For a crown on short tooth stumps only, it is possible, with thepaste, even to model a complete anatomic assembly.

However, a further problem arises from the fact that, although thesolidified compensating paste satisfactorily withstands the pressure ofthe foil, it can be damaged easily in the socketing of the stumps in thepress appliances.

Imbedding in fine lead granulate, which is used in the case of largerjaw models, in fact provides secure standing of the object and permitsthe escape of entrapped air, but is not suitable for small stump modelsbecause the thin mold foil can be damaged easily.

Modelling clays ordinarily are too stiff, cause difficulties insocketing, and do not permit the escape of entrapped air. Layers of foammaterial laid upon the clay permit the entrapped air to escape well, butthe retention of the model stump is insecure and the transition betweenstump and socketing is inexact.

While porous sintered plates formed with several receiving apertures ofdifferent sizes, provide firm retention for the stump models inserteddirectly into these apertures and permit escape of the entrapped air,the transitions between the sinter plate and the stump model are tooright-angled, hard and unyieldable, so that folds form in the pressedmold foil.

SUMMARY OF THE INVENTION This invention relates to the production, bydeformation of plastics foils under fluid pressure, of molds for metalcasting of small dental prosthetic parts and, more particularly, to animproved apparatus for this purpose.

The invention solves the problem of making possible the production ofmolds from synthetic plastics foils by drawing or pressing, even forrelatively small parts, such as crowns or caps, in such a way that thesmall stump models are stably arranged in the drawing or pressing deviceand can be handled easily for preparation, rapid series work and goodexploitation of the foils. The invention further insures that airtrapped beneath the foil can escape satisfactorily, in order to avoidinaccuracies of fit and damage and/or folding of the synthetic plasticsfoil in the base region of the model.

In accordance with the invention, at least one pot-type ves sel, with asupport edge, is provided for insertion into an ap propriate one of anumber of corresponding openings of an insert attachable to the workplate. A kneadable composition is introduced into the vessel and shapedsomewhat conically above the support edge. Thereupon the unpreparedstump model is pressed into this composition and then, after anynecessary preparation of the stump model, fine channels are notched inthe surface of the conically formed imbedding composition, between thebase of the stump model and fine air discharge channels formed in thesupport edge of the vessel. The synthetic plastics foil is then drawn orpressed against the model in the usual way.

With this procedure, all the above-mentioned problems are solvedsatisfactorily, since the use of a kneadable imbedding compositioninsures good stability of the stump model and there is satisfactoryescape of air trapped beneath the synthetic plastics foil so that anextremely high accuracy of fit is attained. In addition, the nature ofthe socketing of the stump model also insures that no fold formation canoccur in the region of the stump base. By the insertion of severalvessels into the insert, particularly into corresponding openingstherein, rapid series work and good exploitation of the foil arerendered possible.

In addition, a simple preparation of the stump model is made possible inthat, after its first pressing into the kneadable composition, thismodel can be withdrawn again for preparation and then reinserted intothe hollow formed by the first pressing-in.

The invention also provides for carrying out of preparation work or finepreparation work, the latter meaning the effecting of fine corrections,upon the stump model after the first or renewed insertion into thekneadable composition by extracting the vessel from the insert, withoutthe necessity to grasp the stump model in any way for this purposevHitherto, it has always been necessary, for this purpose, to take theentire heavy insert, formed directly as a vessel, with the stump modelimbedded therein, in ones hand, which naturally makes specifically finepreparation work very difficult. Additionally, a fine asbestos dough hadproven especially advantageous as the imbedding composition.

The apparatus of the invention includes an insert which is attachable tothe work plate of a foil-drawing or pressing appliance, and which has anumber of openings for the insertion of at least one pot-type vesselhaving a support edge in which there are formed the fine air dischargechannels. These air discharge channels can be formed especially simplyand advantageously as radial incisions in the support edge, arranged atequal angular intervals, and which are narrower then the thickness ofthe synthetic plastics foil utilized, so that blockage of the airdischarge channels cannot occur.

With the generally existing extension of the foils over the support edgeof the vessel, in order to insure escape of air trapped beneath thefoil, it is advisable also to form an air discharge channel system inthe insert, beneath the air discharge channels in the support edge ofthe vessel. Thus, the insert advantageously can be formed with anannular channel and a number of bores opening into the channelperpendicularly thereto and spaced at equal angular intervalstherearound.

It is also preferably to round off the support edge of the potshapedvessel in such a way that, starting from the base of the stump model,and continuing along the conically formed portion of the imbeddingcomposition and the rounded support edge, there is obtained a continuouscurved form, which permits clean application of the foils and thusavoids formation of folds in the foils.

It has been found that if a number of vessels are arranged in one insertfor a drawing or pressing operation, as is especially advantageous forrapid series work, the foil hangs itself up on the individual modelssituated in the vessel, and a relatively deep sagging of the foil occursbetween the individual models. As a result, the compressed air or vacuumforces can act in an approximately horizontal direction upon the foiland cause formation of folds between the individual vessels containingthc.models. These folds can propagate themselves into the base regionsof the models in the individual vessels, whereby the molds obtainedbecome useless. v

In accordance with the invention, a feature is that the support edges ofthe vessels, inserted into the insert, are positioned lower than thesurface of the insert. By reason of this procedure, sagging of the foilat the commencement of the drawing or pressing operation is limited, sothat the vacuum or pressure forces cannot act to any considerable extentin the horizontal direction against the foil. Thus, major distortions orfold formations of the foil are avoided between the individual models.That is to say they at least cannot occur in the region of the actualmodels, and especially not in the base regions thereof. In this case, itis preferable to make the formation such that the surface of the insertis situated approximately at the level of the base of the models, andfurther to make the edges of the depressions, formed in the insert toreceive the vessels, inclined, since this will contribute to thefold-free course of the foil in the molded condition, as far aspossible.

In a particularly advantageous form of the invention, the insert is madein two parts including a lower part which is stationary in relation tothe work plate and receiving the vessels with the support edges restingthereon. The insert includes a second part situated above the lower partand resiliently movable toward the lower part, this second part havingopenings situated above the vessels, in the initial position, with itssurface at the level of, or somewhat below, the heads of the models. Aswill be apparent, the foil, in this embodiment of the invention, issupported over nearly its entire area immediately at the beginning ofthe drawing or pressing operation and until a smooth application of thefoil to the models occurs all over. Thus, sagging and fold formation arecompletely prevented.

In this embodiment also, it is preferable to make the openings of theupper movable part with inclined edges, and to make the formation suchthat the edges of the openings, in the lowered position, cover thesupport edges of the vessels. Thereby especially good foil support isattained, and furthermore the possibility of the foil entering into thefine air discharge channels in the support edges of the vessels isprevented. The last-described embodiment of the invention isadvantageous. above all, because it makes it unnecessary to takeparticular precautions for the escape of air in the insert, since theair trapped beneath the foil can now flow away laterally and freelythrough the fine channels in the surface of the conically formedimbedding compositions and through the fine air discharge channels inthe support edges of the vessels into the space between the two parts ofthe insert and the support edges of the vessels.

An object of the invention is to provide an improved apparatus forproducing, by deformation of plastics foils, molds for metal casting ofsmall dental prosthetic parts.

A further object of the invention is to provide such an apparatusproviding for ready escape of air trapped under the foil.

Another object of the invention is to provide such an apparatus in whichdisadvantageous and unwanted folding and deformation of the foil isprevented.

A further object of the invention is to provide such an apparatus inwhich a pot-type vessel, having a support edge formed with fine airdischarge channels, is inserted into an appropriate opening of an insertattachable to a work plate of a foil deforming appliance.

Another object of the invention is to provide such an apparatus in whicha kneadable composition is introduced into the vessel and shaped toextend somewhat conically above the support edge thereof.

A further object of the invention is providesuch an apparatus in whichthe unprepared stump model is pressed into the composition and eitherretained therein or temporarily removed therefrom during any necessaryrough and fine preparation of the stump model, without the necessity forthe stump model being manually grasped.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a vertical sectional view through apparatus embodying theinvention:

FIG. 2A is a plan view of the pot-type vessel forming part of theapparatus;

FIG. 2B is a partial diametric sectional view through the pot-typevessel;

FIG. 2C is a vertical sectional view of an alternate embodiment of theinvention;

FIG. 3 is a diametric sectional view of the vessel having the imbeddingcomposition introduced thereinto and a stump model inserted into thecomposition;

FIG. 4 is a top plan view corresponding to FIG. 3;

FIG. 5 is a vertical sectional view illustrating an embodiment of theinvention apparatus with a single vessel in an insert and with the foilin the process of application to the stump model;

FIG. 6 is a vertical sectional view of an embodiment of the inventionapparatus with several vessels positioned in one insert and with thefoil in the process of application to the stump models;

FIG. 7 is a view, similar to FIG. 6, illustrating a modified form of theapparatus;

FIG. 8 is a vertical sectional view, similar to FIGS. 6 and 7,illustrating a preferred embodiment of the invention including a twopartinsert, at the beginning of the foil pressing or draw ing operation; and

FIG. 9 is a view similar to FIG. 8 illustrating the apparatus of FIG. 8at the termination of the foil pressing or drawing operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1through 4, a small potlike vessel 1 is provided with an externallyrounded-off support edge 2 having radial incisions 3 formed therein, asparticularly apparent in FIGS. 2A and 2B. Vessel l is insertable into anopening 5 of a lid-type insert 4 which can be attached to the work plate(this is not shown) of an ordinary foil-drawing or pressing appliance.Insert 4 has formed therein, beneath support edge 2 of vessel 1, anannular channel 6 and a number of bores 7 perpendicular to the channel 6and spaced at equal angular intervals from each other, as shown in FIG.I. The incisions 3 are also spaced at equal angular intervals from eachother.

An alternate arrangement is shown in FIG. 2C where a ring of porousmaterial 2a is positioned between the support edge 2 of the vessel 1 andthe edge of the opening 5 in the insert 4.

After vessel 1 is placed in an opening 5 in insert 4, a kneadableimbedding composition 8, which is preferably a fine asbestos dough, isintroduced into vessel 1 and shaped conically above support edge 2,after which a stump model 9 is pressed centrally into the conicallyshaped portion of the imbedding composition. After the first pressing ofstump model 9 into composition 8, the stump model can be withdrawn againand finally prepared, after which it is reinserted into the hollowformed on the first pressing-in, within the composition 8 and withoutany danger of damage to the finally prepared stump model.

After the final insertion of stump model 9 into composition 8, finechannels are notched into the conically shaped surface of composition 8,these channels 10 starting from the base of stump model 9 and extendingto the radial incisions 3 in support edge 2, as particularly illustratedin FIGS. 3 and 4.

If now, and in a known manner, the synthetic plastics foil is pressed ordrawn against the stump model, the air trapped beneath the foil canescape through channels 10, incisions 3, channel 6 and bores 7, so thata satisfactorily fitting shaping of the synthetic plastics foil to themode is insured. Additionally, during all the steps of the method, aprotective and convenient working of the stump model can take place, andsecure seating of the stump model, for the pressing or drawingoperation, is assured.

FIG. 5 illustrates an arrangement wherein only one vessel 1 is used inan insert 4 and, in such case, foil 20 applies itself well on allsurfaces of tooth model 9, on the imbedding composition 8, and on thesupport edge 2 of vessel 1. Thus, formation of folds, especially in theregion of the base of tooth model 9, is avoided.

On the other hand, and as shown in FIG. 6, when there is used an insert4a receiving a number of vessels 1, at the beginning of the drawing orpressing operation, foil 20 sags relatively deeply between theindividual tooth models 9 so that, as a result of the then horizontallyacting pressure or vacuum forces, fold formations in foil 20 can occurbetween the individual models. These can be propagated into the regionof the bases of the models, so that the resulting molds are useless.

FIG. 7 illustrates an improved embodiment of the invention in whichdepressions 17 are formed in an insert 4b, and have the openings forindividual vessels 1 formed in the bases thereof. The edges 18 of theindividual depressions are flattened off or inclined, and the topsurface 19 of insert 4b is situated approximately at the level of thebases of the models 9. Thus, and as illustrated in FIG. 7, the sag offoil 20, during the drawing or pressing operation, is limited, so thathorizontal vacuum or pressure forces cannot act to any appreciableextent upon the foil. Thereby, formation of folds in the foil isavoided, at least in the base regions of the models.

In a preferred embodiment of the invention as shown in FIGS. 8 and 9,there is a two-part insert 4c, the lower part 12 of which isstationarily fitted on the work plate (not shown) of the appliance. Theindividual vessels 1, with supported support edges 2, are inserted intostationary part 12 in the same way as in the embodiment of the inventionshown in FIG. 6.

Above stationary part 12 of insert 4c, there is a movable part 11 whichis lowerable in a direction towards stationary part 12 under the actionof the vacuum or pressure and against the bias of coil springs 13asurrounding guide pins 13. Movable part 11 is formed with openings 14with inclined or bevelled edges 15 above the individual vessel. Asillustrated particularly in FIG. 9, these edges, in the loweredcondition of upper mold part 11, cover the support edges 2 of vessels 1.

As shown in FIG. 8, the initial position of movable part 11 is such thatfoil 20, at the beginning of the pressing or drawing operation, restsnearly uniformly upon the upper surface 16 of movable part 11 and on theheads of tooth models 9. Thus, from the outset, sagging of foil 20,between the individual models, cannot occur, and a completely smoothmold is obtained even between the individual models.

Furthermore, and as indicated by the arrows in FIGS. 8 and 9, the airtrapped beneath foil 20 can flow away laterally through the fine airdischarge channels 3, in support edges 2,

into the space between stationary part 12 and movable part 11 of insert4c, so that no particular air escape precautions need be taken in theinsert per se.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. In apparatus for producing, by the deformation of plastics foil underfluid pressure, pattern molds for shell molds used for metal casting ofsmall dental prosthetic parts, such as crowns and caps, and with which astump model is imbedded in a vessel attachable to a work plate of a foildeforming appliance the improvement comprising, in combination, aninsert attachable to said work plate and formed with a number ofopenings; and at least one pot-type vessel, having an outwardlyextending support edge formed with fine air discharge channels,insertable into an appropriate opening of said insert.

2. In apparatus for producing molds, the improvement claimed in claim 1,in which said air discharge channels are formed as radial incisions insaid support edge and are arranged at equal annular intervalstherearound; said radial incisions being narrower than the thickness ofthe synthetic plastics foils utilized.

3. In apparatus for producing molds, the improvement claimed in claim 1,in which said insert is formed with an air discharge channel systembeneath and communicating with the air discharge channels in saidsupport edge of said vessel.

4. In apparatus for producing molds, the improvement claimed in claim 3,in which said air discharge channel system in said insert comprises anannular channel and a plurality of bores opening into said last-namedchannel perpendicularly thereto and arranged at equal angular intervalstherearound.

5. In apparatus for producing molds, the improvement claimed in claim 1,including a ring of porous material provided between said support edgeof said vessel and the edge of the associated opening of said insert.

6. In apparatus for producing molds, the improvement claimed in claim 1,in which the external surface of said support edge of said vessel isrounded off.

7. In apparatus for producing molds, the improvement claimed in claim 1,in which the support edges of vessels in serted into said insert arepositioned beneath the upper surface of said insert.

8. In apparatus for producing molds, the improvement claimed in claim 7,in which the upper surface of said insert is positioned substantially atthe level of the bases of the models.

9. In apparatus for producing molds, the improvement claimed in claim 7,in which said vessels are inserted in depressions in said insert, theedges of said depressions being bevelled.

10. In apparatus for producing molds, the improvement claimed in claim1, in which said insert is a two-part insert including a lower partpositioned in stationary relation on said work plate and supporting saidvessels through their support edges; said'insert including an upper partpositioned above said lower part and resiliently biased away from saidlower part, said upper part having openings fonned above said vesselsand having an initial position in which it does not extend above thelevel of the heads of the models.

11. In apparatus for producing molds, the improvement claimed in claim10, in which the openings in said upper part of said insert are formedwith bevelled edges which, in the lowered position of said upper part ofsaid insert, cover said support edges of said vessels.

1. In apparatus for producing, by the deformation of plastics foil underfluid pressure, pattern molds for shell molds used for metal casting ofsmall dental prosthetic parts, such as crowns and caps, and with which astump model is imbedded in a vessel attachable to a work plate of a foildeforming appliance the improvement comprising, in combination, aninsert attachable to said work plate and formed with a number ofopenings; and at least one pot-type vessel, having an outwardlyextending support edge formed with fine air discharge channels,insertable into an appropriate opening of said insert.
 2. In apparatusfor producing molds, the improvement claimed in claim 1, in which saidair discharge channels are formed as radial incisions in said supportedge and are arranged at equal annular intervals therearound; saidradial incisions being narrower than the thickness of the syntheticplastics foils utilized.
 3. In apparatus for producing molds, theimprovement claimed in claim 1, in which said insert is formed with anair discharge channel system beneath and communicating with the airdischarge channels in said support edge of saiD vessel.
 4. In apparatusfor producing molds, the improvement claimed in claim 3, in which saidair discharge channel system in said insert comprises an annular channeland a plurality of bores opening into said last-named channelperpendicularly thereto and arranged at equal angular intervalstherearound.
 5. In apparatus for producing molds, the improvementclaimed in claim 1, including a ring of porous material provided betweensaid support edge of said vessel and the edge of the associated openingof said insert.
 6. In apparatus for producing molds, the improvementclaimed in claim 1, in which the external surface of said support edgeof said vessel is rounded off.
 7. In apparatus for producing molds, theimprovement claimed in claim 1, in which the support edges of vesselsinserted into said insert are positioned beneath the upper surface ofsaid insert.
 8. In apparatus for producing molds, the improvementclaimed in claim 7, in which the upper surface of said insert ispositioned substantially at the level of the bases of the models.
 9. Inapparatus for producing molds, the improvement claimed in claim 7, inwhich said vessels are inserted in depressions in said insert, the edgesof said depressions being bevelled.
 10. In apparatus for producingmolds, the improvement claimed in claim 1, in which said insert is atwo-part insert including a lower part positioned in stationary relationon said work plate and supporting said vessels through their supportedges; said insert including an upper part positioned above said lowerpart and resiliently biased away from said lower part, said upper parthaving openings formed above said vessels and having an initial positionin which it does not extend above the level of the heads of the models.11. In apparatus for producing molds, the improvement claimed in claim10, in which the openings in said upper part of said insert are formedwith bevelled edges which, in the lowered position of said upper part ofsaid insert, cover said support edges of said vessels.